The present invention is related to electronic circuit breakers, and more particularly, to methods and devices for testing electronic circuit breakers capable of responding to arc fault and ground fault conditions.
It has been estimated that a large percentage of the fires that occur in residential dwellings can be attributed to xe2x80x9carcing faults.xe2x80x9d An arc fault is an unintentional electrical discharge characterized by an erratic current that may ignite combustible materials. Two types of arc faults which may occur in household wiring include parallel and series arc faults. A parallel fault occurs when there is an arc resulting from direct contact of two wires of opposite polarity. A series fault occurs when there is an arc across a break in a single conductor. Parallel arcing typically occurs where there has been an insulation failure. Series arcs typically result from loose connections and the like. These situations are both outside of the normal range of protection provided by conventional electromechanical or thermal operating circuit breakers. To address this particular type of problem industry has developed the arc fault circuit interrupter (AFCI) technology now being utilized in electronic circuit breakers. A related technology developed to disable a power circuit in the event of a ground faultxe2x80x94typically an unintended leakage current path between a live circuit and a groundxe2x80x94is called a ground fault circuit interrupter (GFCI).
It is well known that electrical arcs are transient events which occur at random and often for very brief durations. Hazardous arcing events are of two kinds: those which result in very large peak currents but which do not trip a breaker because of the very short duration; and those which can result in very low currents but which are continuous in nature and likewise do not trip a circuit breaker. However, some transient events and arc events are non-hazardous such as the high transient current which typically accompanies the start up of a motor or a compressor, or, as often occurs in typical household wiring systems, the small arcs which often accompany the operation of light switches in the home.
Though technology has developed circuit breakers with the capability to distinguish hazardous from non-hazardous arcing and ground faults, testing this capability in production or in actual applications is very difficult because of the wide dynamic range and random nature of arc fault currents. Development of arc testing for circuit breakers has been impeded by the difficulty and/or high cost of generating complex, high current test waveforms at high voltages. What is needed are test devices and methods which operate at low power levels yet are able to simulate accurately and repeatably the properties of arcing faults. Preferably, such devices and methods would utilize the arc fault and ground fault technology built into electronic circuit breakers to provide such testing at a reasonable cost and as simply as possible.
There is disclosed and claimed herein apparatus and a method for testing an electronic circuit breaker having separable contacts and arc fault and/or ground fault interrupting capability responsive to differential currents in the line and neutral conductors, wherein the circuit breaker under test is connected in a test circuit, comprising the steps of: supplying operating power to the source terminals of the circuit breaker wherein the test circuit provides for connecting the neutral conductor source terminal to a ground in the test circuit; coupling testing signals from a test generator in the test circuit to the neutral conductor load terminal of the circuit breaker; and monitoring the condition of the separable contacts in the circuit breaker during the supply of testing signals to the neutral conductor load terminal. In one aspect, the test generator is operated under program control to provide a testing signal sequence to the neutral conductor load terminal of the circuit breaker, which sequence may include a command signal for setting a precondition in the circuit breaker prior to applying testing signals to the circuit breaker under test.